http://llvm.org/bugs/show_bug.cgi?id=9549
Summary: addRequiredTransitive() requires addPreserved().
Product: Documentation
Version: trunk
Platform: PC
OS/Version: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: General docs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
When a pass is added to AnalysisUsage::addRequiredTransitive(), it is also
necessary to preserve this pass. Either through setPreservesAll(),
setPreservesCFG(), addPreserved() or addPreservedID().
When addPreserved is not called and assertions are enabled, the error reported
is:
Assertion `AnalysisPass && "Expected analysis pass to exist."' failed.
At least to me, it was not immediately obvious that this is due the missing
addPreserved call.
So hereby i request this necessity to be explicitly documented at:
http://llvm.org/docs/WritingAnLLVMPass.html#AU::addRequired
Also i would welcome some explanation, why addRequiredTransitive has to be used
"In cases where analyses chain". To me it is even unclear what that means
exactly. I guess it means an analysis-pass using
getAnalysis<some-other-analysis-pass>.
Finally, i would also like some clarification on the difference between
analysis-passes and non-analyis-passes. Something along
"If your pass doesn't modify the program it is an analysis-pass. So you have to
call RegisterPass( , , , true). Only then other passes can make use of your
pass throug getAnalysis()."
(The above paragraph may be entirely wrong of course. If I'd know the
difference, I wouldn't write this bug-report.)
A nice place for this explanation would be
http://llvm.org/docs/WritingAnLLVMPass.html#registration
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